Can Kat's Cartridge Style Engine Block Heater KH11814 Be Left Plugged In Overnight

Updated 09/30/2026 | Published 12/10/2016

Products Featured in This Question

Kat's Heaters Custom Fit Engine Block Heater - Cartridge Style - 120V - 400 Watts

(199)

$69.92

Kat's Heaters Oil or Transmission Pan Heating Pad - 4" x 5" - 120V - 150 Watts

(88)

$58.78

Question:

Is it OK to leave this on the car overnight? Weve been having -8 to -14 degree temps here so want to keep some warmth under the car.

asked by: Tracey V

Expert Reply:

Engine heaters like the Kat's Cartridge Style Engine Block Heater # KH11814 are intended to be left plugged in overnight. Their pad-style oil/transmission pan heaters like # KH24150 also are made to be used this way so that your cold-weather morning starts are easier.

The cartridge heater should not be used with a 100-percent antifreeze solution; the engine should not be started with the heater still plugged in.

expert reply by: Adam R

Brian M.

9/30/2026

What is the reason for not using 100% antifreeze?

Jerry B.

9/30/2026

@BrianM # KH11814 heats the engine coolant directly, and 100% antifreeze doesn’t move heat as well as a normal antifreeze/water mix, so the heater can get too hot. # KH24150 just sticks to the outside of the oil or transmission pan, so it doesn’t care what coolant mix is in the engine.

Brian M.

9/30/2026

@JerryB Thx Jerry. Good to know.